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RF power harvesting (mainly components selection)

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!! the phoenix law !!

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Hello there,
This is my first post here so excuse me if it were not the correct section to discuss what i am going to ask for, anyway, i have the following problem:
I am asked to design a RF power harvesting circuit on PCB board to provide a 1.8v supply with current capability up to 500uA, ripples should be as low as possible, the settling time should be as minimum as possible,
The input is an RF signal with 13.56MHz and peak to peak voltage 100mv, the whole circuit is simply as following: coil antenna->matching circuit->voltage doublers->LDO
later i should include a backscattering block to transmit binary data to the reader

Allright, this was a general description to make everything clear, now i have few questions:
1-which is the best tool to use (the tool should perform both simulations and PCB layout)? i have already started using altium designer but is it good enough? my opinion: yes it is untill now, but i want some professional to advise me
2-I need a discrete 4-terminal mosfet (the usual source, drain, gate and one more connection for substrate however at the worst case a 3-terminal mosfet would be accepted) with low threshold, low parasitics, low on resistance and high current capability, actually this is my biggest problem, i don't have any idea where or how to search for one with these requirement,
hence i would be very grateful if you suggested any part number for this particular mosfet
3-After step 2 (choosing the Tr) i need to find a spice model (with any level but as better as much approved), umm moreover is there anyway to find models for cadence?
4-What is the difference between LDO and normal regulators ?
5- what is back scattering?

Finally, if you have any useful information related to the project i would be very grateful if you informed me, though THE PART NUMBER is the highest priority to me right now

Thanks in advance
 

Backscatter modulation uses a shunt switch at the tuned
antenna to change its return loss to the source / reader.
The same antenna you use to power the tag, so it can't
be so big that it de-Q's the thing.

At 100mV P-P you are needing a zero-VT device and that
is going to back-leak like a sieve when you start to get
any accumulated voltage. Them's the breaks. You should
look at some synchronous rectification scheme that can
boot "well enough" but then swing the gate above and
below ground in sync with the antenna waveform so you
get more efficient rectification. You may need to charge
pump more than 2X to get your 1.8V. Depending on how
much antenna+shunt+charge pump Q you can achieve.
Bearing in mind that if you're sucking out a bunch of
charge your Q will stink, your load-line of the harvesting
portion will as well.

Question whether you need the 1.8V or something lower.
Doing this all on a board seems insane based on what bit
I have learned about RFID tag design. If you are going
to power sizable active circuitry I think you're doomed,
or at best have a lot of work to do in power management.

I doubt you want a discrete MOSFET times N of them.
Lot of capacitance there; the gate, you can make part
of the tank lumped C but some capacitances will be
losers as far as charge pump effectiveness, and beware
any ESD protection and the 3-terminal FETs' body diode.
 
Ok, i think i got the backscattering idea and this is enough for now, umm i have some well designed circuit doing both rectification and charge pumping but the problem as i said before i can not determine which part number should i choose for the mosfet underlying again it should have a body terminal, you are right, this is whole crazy thing to be on a board but this is what my teacher wants and i have to get the job done !! the same reason holds for any other requirement like the 1.8v, ummm regarding the power it is almost 1mw, i don't think this is too much, right? so let me try to understand some points, how much capacitance do you think i need? which part number should i choose for the FET's (at least how to search for it on digikey since i can't?), ah by the way, the 100mv peak to peak is the rectifier input not the antenna voltage, my concern right now is the rectifier only, antenna and its matching should be considered later
Thanks for your help and excuse me if i could not match you, i am still learning, this is a completely new experience for me :smile:
 

Before designing a circuit, you should verify that the input source is supplying sufficient power. 1.8V/500 µA corresponds to about 1mW, a source with a loaded output voltage of 100 mVpp (35 mV rms) would have a source impedance of only 1.25 ohm, which sounds rather unlikely. So what's the actual source impedance and has the 100 mVpp been measured with or without a load resistor?
 

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